Tractor unit for industrial trucks



I. F. SCHRECK TRACTOR UNIT FOR INDUSTRIAL TRUCKS Dec. 14, 194?.

Filed 001:. 7, 1941 2 Sheets-Sheet l INVENTOR Irvin E Schreaais BY 7M 5.W

ATTORN EY Patented Dec. 14, 1943.

@NHEQ STATES PAT ENT- OFFICE rnsc'roa' UNIT roa mnus'rmsr. raucxs IrvinF. Schreck. .Cleveland Heights, Ohio Application mm '1. 1941, Serial.No. 413,960

(01. let-4s) i5 Claim. This invention relates to tractor units forindustrial trucks and, more particularly, to the. propelling mechanismand the controlling means therefor.

The invention has for an object to provide a tractor unit in which .thetraction wheel driving mechanism consists of a driving motor and aclutch controlled, reversible driving mechanism interposed between themotor and wheel, and in which the motor and mechanism are compactlymounted upon a relatively small supporting platform on the frame of theunit adjacent the traction wheel with the reversible driving mechanismoccupying a narrow space alongside the motor.

The invention has for a further object to provide an inexpensive andcompact clutch controlled, reversible driving mechanism for a tractorunit which is adapted to be controlled by a simple, manually operableclutch actuator.

A further object is to provide the tractor unit with a draft tongue bymeans of which the truck may be drawn manually, the tongue having clutchcontrolling means mounted thereon, by which the Figure 1 is a sideelevationof a tractor unit embodying the invention and showing thetractor Fig. '1 is a sectionalyiew on an enlarged scale 4 taken on theline-indicated at lin Fig. 6;

Fig. 8 is a section on an enlarged scale taken;

on theiine indicated at 8-4 In Fig. 6; and

Fig. 9 is a section similar o Fig. 8 showing the shifter collar v"andthrust pin in clutch engaging f position.

operation of the driving mechanism may be controlled by the operator.

A further object is to control the reversin mechanism by swingingmovements of the draft tongue in such manner that the truck cannot bepropelled toward the operator when the draft tongue is moved to itsuppermost position, but

which will permit the truck to be propelled in a rearward direction withthe draft tongue in its uppcrmost position. vnfl'FiillZhBlifiii'fijEOliS ar'eto provide a clutch contmued lversiilgdfive forzthe traction wheel --through friction clutch elements whichhave on y 7 a slight axial movement between their engaged and disengagedpositions and which free themselves as soon as-axial pressureisreleased.and to provide simple and conveniently operable means for controllingsuch clutches.

' A further object is to provide a simple chain and sprocket drive forthe traction wheel, which includes a clutch operated reversing means.With the above and other objects in view, the

inventionmaybe said to comprise the traction unit as illustrated in theaccompanying drawings, hereinafter described, and particularly act forthin the appended claims, together with such variations and modificationsthereof that will be aD- parent to oneskilled in the art to which theinvention pertains.

Reference should be had to the accompanying drawings forming a part ofthe specification, in which:

Referring to the accompanying drawings, the tractor unit of .thepresentinvention is shown mounted in the forward end of a truck frame I. Thetractor unit is mounted in the truck frame I to turn about a verticalaxis, the frame 8 of the tractor unit being rotatably mounted in anannular bearing member 2 at -the forward end of the frame I and beingprovided with an annular the same as in the truck shown and described inmy Patent No. 2,209,356, granted July so, 1940.

A draft tongue 8 is connected by a horizontal pivot l to the tractorunitframe 8 and by means of this tongue the tractor unit may be turnedwithin the bearing "portion 2 of the truck frame to steer the truck,and-the truck may be drawn forwardly or pushed rearwardly by means ofthe tongue 8, when. .desired. The downward movement of the tongue Q islimited by engagement of 1 the tongue-with a bumper bar 'I at theforward end of the tractor unit frame I and the tongue .may bedetachably secured in its uppermost, substantially vertical position bymeans of a latch O pivotally mounted on the bumper bar 8 and looselyengaging 9. lug II adjacent the rearward end of the tongue I.

The tractor unit frame has a platform I I which provides a support for adriving motor l2, which may be an internal combustion engine. Through'|1 are clamped between the and 22, clutch disks 3| 4|. Anidler-sprocket 43 is suitable gearing in a reduction gear housing i3,the motor |2 drives a horizontal shaft |4 above the rear end portionplatform II, the shaft |4 having a sprocket I5 attached thereto, throughwhich the propelling mechanism is driven. Forwardly of the shaft l4, twovertically'spaced shafts i6 and I1 are mounted between inner and outeruprights l9 and i9 attached to the platform The outer upright i9 is inthe form of a plate extending substantially the full length of theplatform along an edge thereof. The inner upright I9 is a narrower platedisposed between a portion of the motor l2 and the forward end of theplatform The shafts l9 and uprights l9 and i9 by means of bolts 29 whichuprights 9 and 9 and screw in the ends of the shafts.

Adjacent the outer upright |9, clutch elements in the form of frictiondisks 2| and 22 are rotatably mounted upon the shafts 5 and I1. Thedisks 2| and 22 are provided with ball thrust bearings 23, the innerrings washers 24 clamped between the upright l9 and the outer ends ofthe shafts l9 and I1. On their inner sides, the disks 2| and 22 haveflat friction faces 25, and to the outer sides of the disks sprockets 26and 21 are rigidly attached to the disks 2| and 22 by means of screws29. A sprocket chain 29 extends over the sprockets I5, 26 and 21 so thatwhen the sprocket I5 is driven by the motor l2, the sprockets 26 and 21are continuously rotated in the same direction. Adjacent to and inwardlyof the clutch disks 2| and 32 are mounted, disks 2| and 3| providing apair of coacting clutch elements on the upper shaft l9 and the disks 22and 32 providing a similar pair of clutch elements on the shaft l1. Thedisks 3| and 32 are provided-with ball thrust bearings 33, the of whichare slidable on the shafts 5 engageable with thrust washers 34 on theshafts i6 and H. The disks 3| and 32 are provided with flat facing rin s35 composed of suitable friction material which are engaaeable with thefaces 25 of the disks disks 3|' or 32 axially toward the opposed disks2| or 22, either of the disks 3| or 32 may be caused to turn in unisonwith the motor driven disk on its shaft. S rockets 36 and 31 are rigidlyinto threaded bores and 1 and attached to the disks 3| and 32 by meansof screws 39. The clutch disk 3| of the upper pair is ada ted to bepressed into en a ement w th the disk 2| by m ans of a. shifter collar39 slidable on the sh ft l6: and the disk 32 on the lower shaft H is adted to be ressed into clutchin en a ement w h the d sk 2 b means of a shfter collar lllslidably mounted on the shaft |1 immediately beneath thecollar 39,

A sprocket 4| is attached to the traction wheel 4 and a s rocket chain42 extends around the sprocket 36 on the u er shaft l9 and the sprocketzontal shaft 44 and is positioned intermed ate the shafts l9 and i1 andforwardly thereof. The sprocket chain 42 extends over the idler sprocket43 and rearwardlv therefrom with its exterior engaging the sprocket 31on the shaft |1 through an arc of contact sufllcient for effectivedriving engagement. When the upper pair of clutch ,elements 2| and 3|are engaged, the'sprockets 26 and 36 are simultaneously rotated in thesame direction and the chain 42 and the traction wheel 4 are driventhrough the sprocket 36. When the extend through the.

inner races 2| and 22. By pressing either of themounted on a horiofwhich bear against each shaft pair of clutch elements 22 and 32 on thelower shaft H are engaged, the sprockets 21 and 31 are rotated in unisonand the chain 42 is driven through the sprocket 31. By reason of thefact that the sprocket 36 engages the interior of the sprocket chain 42while the sprocket 31 engages the exterior of the sprocket chain 42, thechain 42 is driven in one direction through the sprocket 36 when thesprocket 36 is clutched to the sprocket 26 and in the opposite directionthroughthe sprocket 31 when the sprocket 31 is clutched to the sprocket21.

In order to maintain the proper tension in the sprocket chain 42, thesprocket 43 may be mounted in any suitable way for horizontal ad-Justment. As herein shown, the sprocket 43 is mounted on a shaft 44which is clamped between the uprights 9 and 9 by means of bolts 45extending through horizontal slots 46 in the up rights l9 and i9. Byproperly positioning the bolts 45 in the slots 46 before clamping theshaft in place, the sprocket 43 may be adjusted to take up any slack inthe sprocket chain 42. The engine is attached to the platform H by means01' suitable anchoring bolts 41, which pass through longitudinal slots49 in the platform. By adjusting the engine on the platform beforetightening the bolts 41, the proper tension may be applied to thesprocket chain 26.

The shifter collars 39 and.49 have integral, forwardly extending arms 49and 59 which are connected by a link 5| so that the collars 39 and 49are constrained to turn simultaneously in the same direction. Stationarycollars 52 and 53 are interposed between the shifter collars 39 and 49and the inner supporting standard l8. The collars 52 and 53 are providedwith peripheral projections 54 which engage with fixed lugs 55 on thesupporting standard I9 to hold the collars 52 and 53 against turningmovements on the shaft. The shifter collar 39 and adjacent stationarycollar 52 on the upper shaft 6, and the shifter collar 49 and adjacentstationary collar 53 on the lower shaft H are provided on their opposedfaces with circumferentially spaced recesses 56 and 51, which provideseats for opposite ends of thrust pins 59. The pins 59 between the twocollars on are regularly spaced about the aids of the collars at aninclination to the opposed faces of the collars. The pins 59 engagingeach of the shifter collars 39 and 49 are so disposed that upon turningmovement of the collar in one direction the pins move toward a positionparallel with the axis and exert an axial thrust on the collar. Thethrust pins v59 engaging one shifter collar are inclined oppositely tothe pins engaging the other shifter collar so that pressure isapplied'to one collar when it is turned in one direction and to theother collar; when it is turned illustrated in the .drawingsrthe pins 59interposed between the l and pressing the clutch element 3| into engage-I ment with the clutch element 2|. arms49 and 59 are pins 59 interposedbetween 49 and 53, which are oppositely disposed with respect to,thepins between the collars on the upper shaft, apply axial pressure I tothe collar 5 49, engaging the clutch elements 22 and 32. Thus, by movingthe arms 49 and 59 upwardly or down-- assess:

wardly and the lifting oi the arms II and: It to clutch the sprockets I1and 81 is'prevented, so

ments and to compensate for wear between the friction faces of theclutch elements, shims 59 may be inserted between the thrust collars 5 2and 53-and the supporting standard [8.

At its forward end, the draft tongue 6 isprovided with a transversehandgrip portion 60, upon which is rotatably mounted a sleeve iii. Thesleeve 6! has a projecting lug 62, to which one end of a rod 63 ispivotally attached. The opposite end of the rod 53 is pivotallyconnected to the outer end of the lower forwardly projecting that withthe tongue in this position the truck cannot be propelled forwardly. Thesleeve ll, however, isfree to turn ina clockwise direction when thetongue is in its uppermost position, so

that the operator may cause the truck to be propelled rearwardly whenthe handle is in this position.

. To enable the operator to bring the truck quickly to a stop, a brakeis provided which is'controlled by the draft tongue 6. The brake devicecomprises a bar 66 which is slidably mounted on the frame 8 and guidedby the pivot I. and a pin 61 on the frame! adjacent the periphery of thewheel, the bar to carrying a brake shoe 8 which is brought intoengagement with the pe-- I riphery of the wheel upon a pivotal movementof the tongue 6. The bar 08 carries an adjustable abutment in the formof a screw 09. which is adapted to be secured in adjusted position 'byarm 59. The operator by gripping the sleeve'ol and turning the same in acounterclockwise direction; as viewed in Fig. 1, lifts the arms as and59, clutching the sprocket 31 to the sprocket 2? to propel the truckforwardly. Upon turning movement of the sleeve Si in a clockwisedirection, the arms 59 and 5!] are moved downwardly to clutch thesprocket as to the sprocket 26 to propel the truck rearwardly.

Whenever the truck tends to overtakethe operator walking ahead of thetruck holding the handgrip of the tongue, the tongue b will be movedtowards vertical position and means is provided for controlling theoperation of the driving mechanism by the tongue to automatical-- lymove the clutch actuators to neutral position to prevent injury to anoperator. the operating connections being so arrangedsthat when thetongue approaches its uppermost position, as shown in dotted lines inFig. 1, the shifter collars are held against movement in a direction toem gage the clutch through which the truck is pro elled forwardly.Suitable means is provided for limiting the turning movements of thesleeve 6 I with respect to the handgrip dd, sb that in the uppermostposition of the tongue the sleeve 8i is normally in itsneutral positionand is movable in one direction only from its neutral position.

, As shown in Fig. 1 of thedrawings, the rod 83 bears against the.sleeve Bl when the rod is in vertical position prevents turning of thesleeve in a counterclockwise direction. To provide for disengagement ofthe clutch through which the truckis propelled forwardly at the tongue,the handgrip portion 60 of the tongue may be provided with a radial pin84, which exmeans of a nut .10. The head of thescrew as is in the pathof movement of a lug -H on the tongue 8 and is engaged by the lug "H asthe tongue 8 approaches its vertical position. By pressing the upper endof the tongue t toward the truck, pressure is applied throughthe barlatch in locking position to permit the applica tion of the brake. Uponrelease oi the pressure exerted by the draft tongue thebrake is brushedaway from the wheel tread when the wheel ro-' tates.

g A fuel tank 12 may bemoan-ted upon the upper I end or the outerstandard is and suitable bracket 13 attached to the standard.

The operator by gripping the sleeve 8! and;v exerting a forward pull onthe draft tongue can, t with little efl'ort, turn the sleeve in adirection to exert a pull upon the rod 63, lift thearm's 49 and 50, andengage the lower clutch to-propel the truck forwardLv. Likewise, bygripping the sleeve 4 BI and exerting a rearward push, the rod" isactuated with little eiiort to move the arms and 50 downwardly andengage the upper clutch Y to propel the truck rearwardly. By maintainin"his grip on the sleeve" after initial actuation,

the necessary pressure may be maintained upon the engaged clutchelement. At any timethe traction wheelmay. be released fromthe drivingdesired point in the movement of the draft mechanism by merelyreleasingthe sleeve SI and the truck may be quicklystopped by swingingthe draft tongue to .brake-applying position. a

The present invention provides a simple and compact self-propelledtractor j uni-t having a clutch controlled reversingmechanism controlledI by actuators which are directly. connectedto optends through anarcuate slot in the sleeve ti.

The pivotal connectionfbetween the arm Bil and the actuating rod 63 isspaced from the pivot I of the tongue so that vertical swingingmovements of the tong 8 cause the handgrip portion 80 to turn wi hid thesleeve 6!. The pin $6 and the slot 65 are so arranged that when thetongue approaches its uppermost position the pin 63 engages with an endof the slot 65,'so that further turning movement of the handgrip tiiwithin'the sleeve is prevented. The range of erating members on'thedrait tongue in such a way'as to provide .a convenient and safecontrol of the driving mechanism by an operator walking invthe directionof travel of the truck and'guiding its movementby means of the drafttongue. I

It is to be understood that variations and modifications. oil the!specific] devices herein shown and described for purposes ofillustration", may be'made withoutdeparting from the spirit of theinvention. WhatIclalm is:

1. A tractor unit'comprising' a irama atrao- 7 tion wheel. journaled inthe irame. a draft tongue pivoted at its rearwatdend to the frame toswing about a horizontal axis, a motor carried by the frame, means fordriving the traction wheelfrom V able upwardly or downwardly said motorincluding a clutch controlled reversing mechanism, means for operatingsaid clutches including an operatingmember mounted for movement ineither direction from a neutral psition to cause said unit to bepropelled forwardly or rearwardly, an actuating member movably mountedon said tongue, a rod connected to said actuating member and pivoted tosaid clutch operating member laterally of the pivotal axis of the tonguewhereby said actuating member is moved relatively to the tongue upon aswinging movement of said tongue, and means for limiting the movement ofthe actuating member in one direction with respect to the tongue torestrict the movement of said clutch operating member to a movement inone direction from neutral position when said tongue is in its uppermostposition.

2. A tractor unit comprising a frame, a traction wheel journaled in theframe, a draft tongue pivoted at its rearward end to the frame to swingabout a horizontal axis, a motor carried by the frame, means for drivingthe traction wheel from said motor including a clutch controlledreversing mechanism, means for operating said clutches including anoperating member mounted for movement in either direction from a neutralposition to cause said unit to be propelled forwardly or rearwardly, anactuating member mounted upon said tongue and operably connected to saidclutch'operating member to actuate the same in either direction, andmeans conrolled by swinging movements of said tongue for preventingactuation of said clutch operating member in a direction to propel saidunit forwardly when said tongue is in its uppermost position.

3. A tractor unit comprising a frame, a trac tion wheel journaled in theframe, a draft tongue connected at its rearward end to said frame toswing about a horizontal axis, said tongue having to said sleeve andpivoted to said clutch operating member, the pivot connecting said rodand clutch operating member being spaced from the pivotal axis of thetongue, whereby said handgrip portion turns within the sleeve as thedraft .tongue is swung vertically, and means for 1imiting the turningmovement of the sleeve with respect to the handgrip portion to restrictthe range of movement of said control member when said draft tongue isin its uppermost position to a movement downwardly from neutralposition.

5. A tractor unit comprising a frame; a motor carried by the frame, atraction wheel journaled in the frame, a draft tongue pivoted to theframe, two spaced parallel shafts mounted in the frame, a pair of clutchelements mounted on each shaft, a driving connection between said motorand one clutch element of each pair for continuously rotating the latterclutch elements, a driving connection between each of the other twoclutch elements and said wheel, one of said driving connections being areverse driving connection, clutch operating means including anactuating member movable in one direction from a neutral position toengage the clutch elements of one pair and in the opposite directionfrom said neutral position a transverse handgrip portion adjacent itsforward end, a motor carried by the frame, means for driving thetraction wheel from said motor including a clutch controlled reversingmechanism, means for operating said clutches including a clutchoperating member mounted for movement in either direction from a neutralposition to cause the unit to be propelled forwardly or rearwardly, asleeve rotatably mounted on said handgrip portion, an actuating rodconnected eccentrically to said sleeve and pivoted to said clutchoperating member laterally of the pivotal axis of the tongue wherebysaid handgrip portion turns within said sleeve as said tongue is swungvertically, and means for, limiting the turning movement of the sleevewith respect to said hand grip to restrict the movement of said clutchoperating member to a movement in one direction from neutral positionwhen said draft tongue is in its uppermost position.

4. A tractor unit comprising a supporting frame, a traction wheel, adraft tongue connected at its rearward end to said frame to swing abouta horizontal axis, said tongue having a transverse handgrip portionadjacent its forward end, a motor mounted on the frame, means includinga clutch controlled reversing mechanism for driving said traction wheelfrom said motor, means for operating said clutches including avertically movable clutch operating member movfrom a neutral position topropel the unit forwardly or rearwardly, a sleeve rotatably mounted onsaid handgrip portion, an actuating rod connected eccentrically toengage the clutch elements of the other pair, whereby said wheel may bedriven in a forward or reverse direction, and means carried by saiddraft tongue for operating said actuating member 6. A tractor unitcomprising a frame, a motor carried by the frame, a traction wheelJournaled in the frame, a draft tongue pivoted to the frame, two spacedhorizontal shafts mounted in the frame, a pair of clutch elements havingopposed friction faces mounted side by side on each shaft, one clutchelement of each pair being slidable upon the shaft to engage ordisengage said friction faces, a driving connection between the motorand one clutch element of each pair for continuously rotating the latterclutch elements, a

driving connections being a reverse driving connection, means forpressing together the friction faces of the clutch elements of eitherpair including an actuating member movable in one direction from aneutral position to engage the clutch elements of one pair in the otherdirection from said neutral position to engage the clutch elements ofthe other pair, whereby said wheel may be driven in a forward or reversedirection, and means carried by said tongue for operating said actuatingmember.

7. A tractor unit comprising a frame, a motor carried by the frame, atraction wheel Journaled in the frame, a draft tongue pivoted to theframe, two spaced horizontal shafts mounted in the frame,.a pair ofclutch elements having opposed friction faces mounted shaft, one clutchelement of each pair being slidable upon the shaft to engage ordisengage said friction faces, a driving connection between the I motorand one clutch element of each pair for continuously rotating the latterclutch elements, a driving connection between each of the other twoclutch elements and said wheel, one of said driving connections being areverse driving connection, a collar slidably and rotatably mounted oneach of said shafts adjacent each of the slidable clutch elements, anarm attached to each collar, a link connecting said arms to cause thecollars to turn simultaneously in the same diside by side on each" lo:pressing the letter c uel to? position ueon turning movemeot fiffi. theopgoelte zllrseotioo. from sold neutral position, en eetuating membercarried by said. tongue and connected to one of sold ems.

8. A tractor unit comprising o frame, a mo tor carried by the frame,traction wheel loot mled in the ifrme, tongue plvoteclvto the frame, twospaced horizontal shafts mounted in the frame, a pair oz clutch elementshaving opposed friction ioces mounted side by slcle on each shaft, oneclutch element of each pelt be ing slicleole upon the shaft to engage or:llsem gage sold friction feces, a, driving connection l2o= tween themotor one clutch element 0;? eee pair for cootinuously rotating linelatte? e111 oh elements, a drivz'zzg connection between each of theother two clutch elements one said wheel, one oi sold dri lingooxzoeotloes 'oelog e firevelree ozmlng connection, a collar umm one.zoo ome bly moo-med on each of solo edjeoe'ot each of the stidebleolutoh elements, 22o arm toehed to eeeh oollee, link cementing some tocause the sell to ii-om elmultezleottely in the some dlreotioo, meeoe aone oollor end ltioe 21w olutoi o 20*: oellee e sexing position noon atmovement in one direction 3mm a neutral pesl tloo, means loterposeclbetween, other oollslr and one frame for the letter collar to clot-2&1eogeglog position upon o movement to the o o oosl'to weet-loo from solo.:oeulsel poeltloo, :emfigflo l the outer em sold Isms, o at re :5 or,sold oozg and on slowest-*5;

o sold ite opposite eeel to A tractor; omit some-rising a freeze, e,mote? the frame, on txeotloo wheel loomfleoone olut two home, olivinesolo traction wheel to peopel forwardly including o pair, of relativelymovable friction clutch elements on one oi said shafts,

means for driving sold traetion Wheel to propelthe unit rearwazdlyincluding o pair of relatively movable friction elutoo elements oo. theof shaft a sleeve rotetobly mounted on sold 1' mp portion, and meansoperated. by sold. sleeve for engaging the olutch elements on onesl'loit noon o tuming movement, of the sleeve in one direotloo. one forengaging the olutclo elements on the other shaft upon e, turningmovement of l the sleeve in the opposite direction,

11. tractor unitcomprlslng e Home, tree t'loo wheel journeled in theflame, e draft tongue golvotelzlet its rearward end to the frame toswing about e horizontal ems, o motor carried by the Zreme, moons fordrlvlzog the traction wheel from eelcl motor looludiog o, clutchcontrolled reversing mechanism, two specell. parallel shafts momltecl .v

on eelo. Home means for driving sold traction to ozopel the unitforwardly including wheel jourmled m solo l'mme, two epeceo eholtemoomaeel to the Home oleove emfl porellel tvlti'o the em of sold wheel,e clutch, element rotot momztetlon eeoo of? soicl e l lofts, m

tefegzoseel b tween the motor elo, clutch ele or M View tweeter tmoloomprieieg a one, motor oexrled izeme, o

disks for driving both clutch disks in the same direction, a secondclutch disk rotatably mounted on each shaft alongside the motor drivenclutch disk, the two clutch disks on each shaft being relatively movableon the shaft into and out of clutching engagement, mean for shiftingsaid movable clutch disks including a movable operating member and meansconnecting member to a clutch disk of each pair or: ale to engage onepair of clutch disks upon are vcment of said member in one directionfrom a neutral position and to engage the other pair of clutch disksupon movement of said member in the opposite direction from said neutralposition, a wheel driving sprocket, a sprocket attached to each of saidsecond clutch disks, and a sprocket chain extending around said wheeldriving sprocket and one of said disk attached sprockets and having itsexterior in driving engagement with the other of said disk attachedsprockets, whereby said traction wheel may be driven in one direction byone of said disk attached sprockets or in the opposite direction by theother,

14. A tractor unit for trucks comprising a frame, a motor carried by theframe, a traction wheel Journaled in the frame, a wheel drivingsprocket, a motor driven sprocket, two spaced shafts mounted in theframe, a pair of sprockets rotatably mounted side by side on each ofsaid shafts. the sprockets of each pair having opposed clutch elementsattached thereto, one sprocket of each pair being slidable upon theshaft toward and away from the other sprocket oi the pair to engage ordisengage the clutch elements, a sprocket chain engaging one sprocket oieach of said pairs and the motor driven sprocket, a

asaaeaa gagement With'the sprocket 'with which it engages on the othertot said shafts, and means for' shifting the move. Ti sprocket of eitherof said pairs to clutch the sprockets of the pair together.

15. A tractor unit comprising a frame, a trac tion wheel journaled inthe frame, a motor carried by the frame, two spaced parallel shaftsmounted on said frame, mean for driving said traction wheel to propelthe unit forwardly including a pair of relatively movable frictionclutch elements on one of said shafts, means for driving said tractionwheel to propel the unit rearwardly including a pair of relativelymovable friction clutch elements on the other shaft, a collar mounted toslide and turn on each of said shafts adjacent the movable clutchelements on each shaft, mean associated with one collar for slid-. ingthe collar on the shaft to engage the adjacent pair of clutch elementsupon turning movement in one direction, means associated with the secondcollar for sliding the same on the shaft to engage the other pair ofclutch elements upon a turning movement in the opposite direction, andmeans for simultaneously turning the two collars in either direction toclutch one or the other pair of clutch elements.

IRVIN F. SCHRECK.

